1. Field of the Invention
The present invention relates to an arrangement or device for fixing a piston, or a piston rod attachment to a piston rod. The inventive configuration includes one of these three members to have a hole running in its axial direction and the other of the joining components having a portion configured to be received by the hole for effecting connection of the piston or the piston rod attachment and the piston rod. The actual connective device or arrangement includes an elongate locking means or member, at least one first opening in the piston or the piston rod attachment and at least one second opening in the piston rod. These openings extend in a different direction from the axial direction and are designed for receiving the locking means or member for the purpose of bringing about fixation. The invention can, for example, be applied to both hydraulic and pneumatic cylinders. The invention also relates to a method for establishing the fixation.
2. Background
The specification of U.S. Pat. No. 6,032,569 describes a device for fixing a piston to a piston rod. The piston is provided with a threaded axial through-hole intended for receiving a corresponding externally threaded portion of the piston rod. The piston is also provided with a portion of reduced diameter through which the hole extends. This narrower portion is provided with a number of radial through-openings that open into a groove extending in the circumferential direction. The piston rod is, close to its end, provided with a number of axially running grooves. For fixing the piston on the piston rod, the piston rod is screwed into the piston in such a manner that one of the openings coincides with one of the axial grooves. The device also includes a locking clamp which is, in principle, C-shaped. One end portion of the clamp projects from one end of the C-shape essentially in the direction toward the other end of the clamp. The locking clamp also has such resilient properties that the ends of the clamp can be positioned at different spacings relative to each other. When the piston has been screwed to the intended location on the piston rod, the locking clamp is clamped firmly in such a manner that the end portion of the clamp passes through the opening in the narrower portion of the piston and down into the groove of the piston rod. The clamp is thus clamped firmly in the groove running in the circumferential direction around the portion of reduced diameter. In this way, the piston is rotationally fixed relative to the piston rod.
A first object of the invention is to produce a construction that is simple and cost-effective, in terms of production, for fixing a piston or a piston rod attachment to a piston rod.
This object is achieved by virtue of the elongate locking means or arrangement having a greater extent in its transverse direction, along at least a part thereof, than the extent of at least one of the openings in its transverse direction, along at least a part thereof, for form locking between the locking means and the opening. Only a simple tool, for example a hammer, is needed for putting the locking means in place. With this type of construction, a strong fixing device, which is possible to assemble rapidly and easily, is obtained at a low production cost.
According to a preferred embodiment, the piston or the piston rod attachment is provided with the hole that is at least partly threaded. The piston rod is configured so that the portion intended for being received in the hole of the piston includes a threaded portion corresponding to the threadings of the hole of the member to be joined thereto. This connection type is reliable and cost-effective from a manufacturing point of view.
According to another preferred embodiment, the first opening has a longitudinal extent at least essentially at right angles to the axial direction of the piston or the piston rod attachment and is also open in the axial direction thereof. In other words, the first opening consists of a slot or a groove, and is therefore open in the axial direction of the piston or the piston rod attachment. Such an opening can be produced in a number of different ways, inter alia, by casting or by milling which allows scope for simplified and thus cost effective manufacture.
According to another preferred embodiment, the piston or piston rod attachment has a portion of reduced diameter projecting in its axial direction, and the first opening extends through this portion. The piston or the piston rod attachment also has at least one set of two of the first openings, which extend through the body of the projecting portion, and the longitudinal direction of which extends along an at least essentially straight line. Opportunities are thus afforded for fixing the locking means at two points on the piston or the piston rod attachment, which provides increased functional reliability.
According to another preferred embodiment, at least one of the piston or the piston rod attachment and the piston rod includes a shoulder intended for interaction with a portion of corresponding design of the other of the piston or the piston rod attachment and the piston rod for the purpose of limiting the axial movement of the piston rod relative to the piston or the piston rod attachment. By virtue of, during connection of the piston or the piston rod attachment and the piston rod, first bringing these together so that the shoulder is brought into contact, and then moving the piston or the piston rod attachment relative to the piston rod in another direction so that the shoulder no longer makes contact and in this position making the first and second openings coincide and inserting the locking means into these openings, the axial forces which arise when the piston works in the cylinder will be taken up by the threads of the piston and/or the piston rod attachment and the piston rod and not by the locking means. This reduces the risk of fatigue damage.
Another object of the invention is to bring about a method for fixing a piston or a piston rod attachment to a piston rod that allows simplified mounting in relation to the known art. A further object of the invention is to bring about a method for fixing a piston rod attachment to a piston rod which affords opportunities for cost-effective manufacture of the parts necessary for fixing.
Further advantages and advantageous embodiments of the invention emerge from the description below and the patent claims.